According to size reduction and high performance of mobile equipment, as an inductor used in a power source circuit as a DC-DC converter application, a laminated power inductor advantageous for size reduction is being used. In recent years, there is a trend toward further great current, which results in requirement for a lower direct-current resistance characteristic as the specification for an inductor.
As the technique for lowering the direct-current resistance, there is setting a sectional area of an internal conductor large and a line length short. However, when the width of the conductor is made wide as the technique for making the sectional area large, an area through which magnetic flux passes decreases, which results in lowering of an inductance value. Further, when the thickness of the conductor is made large, the inductor tends to be affected by stress due to a difference in shrinkage ratio and a difference in shrinkage process between an internal conductor and a ferrite material during burning shrinkage, and a difference in linear shrinkage therebetween, or the like, which causes a structural defect such as a crack.
As a means for solving this problem, for example, a technique of connecting conductor patterns in parallel to reduce a direct-current resistance without setting the thickness of a conductor thick is disclosed in Japanese Unexamined Patent Application Publication, First Publication No. H8-130115. In the technique disclosed in Japanese Patent Application Laid-Open No. H08-130115, however, the conductor locally becomes significantly thick due to joining four upper and lower layers at conductor connecting portions, which results in such a problem that the locally thick portion tends to constitute a starting point for a structural defect such as a crack.
Further, in Japanese Patent Publication No. 4973996, a technique of combining a conductor pattern formed in ¾ turns to 1 turn and a conductor pattern formed in 1 turn to connect them in parallel is disclosed. In the technique disclosed in Japanese Patent Publication No. 4973996, however, there is such a problem that a portion where only one conductor pattern layer (a portion where the conductor patterns are not parallel) is provided exists, where a direct-current resistance considerably increases.